BOSTON (Reuters) - EBay Inc
said that hackers raided its network three months ago,
accessing some 145 million user records in what is
poised to go down as one of the biggest data breaches in
history, based on the number of accounts compromised.

It advised customers to change their passwords immediately, saying
they were among the pieces of data stolen by cyber criminals who
carried out the attack between late February and early March.

EBay spokeswoman Amanda Miller told Reuters late on Wednesday that
those passwords were encrypted and that the company had no reason to
believe the hackers had broken the code that scrambled them.

"There is no evidence of impact on any eBay customers," Miller said.
"We don't know that they decrypted the passwords because it would
not be easy to do."

She said the hackers gained access to 145 million records of which
they copied "a large part". Those records contained passwords as
well as email addresses, birth dates, mailing addresses and other
personal information, but not financial data such as credit card
numbers.

Miller also said the company has hired FireEye Inc's Mandiant
forensics division to help investigate the matter. Mandiant is known
for publishing a February 2013 report that described what it said
was a Shanghai-based hacking group linked to the Peoples Liberation
Army.

EBay earlier said a large number of accounts may have been
compromised, but declined to say how many.

Security experts advised EBay customers to be on the alert for
fraud, especially if they used the same passwords for other
accounts.

"People need to stop reusing passwords and should change their
affected passwords immediately across all the sites where they are
used," said Trey Ford, global security strategist with cybersecurity
firm Rapid7.

Michael Coates, director of product security with Shape Security,
said there is a significant risk that the hackers would unscramble
the passwords because typically companies only ask users to change
passwords if they believe there is a reasonable chance attackers may
be able to do so.

Still, eBay said it had not seen any indication of increased
fraudulent activity on its flagship site and that there was no
evidence its PayPal online payment service had been breached.

EBay said the hackers got in after obtaining login credentials for
"a small number" of employees, allowing them to access eBay's
corporate network.

It discovered the breach in early May and immediately brought in
security experts and law enforcement to investigate, Miller said.

"We worked aggressively and as quickly as possible to insure
accurate and thorough disclosure of the nature and extent of the
compromise," Miller said when asked why the company had not
immediately notified users.

The breach could go down as the second-biggest in history at a U.S.
company, based on the number records accessed by the hackers.

Computer security experts say the biggest such breach was uncovered
at software maker Adobe Systems Inc in October 2013, when hackers
accessed about 152 million user accounts.

It would be larger than the one that Target Corp disclosed in
December of last year, which included some 40 million payment card
numbers and another 70 million customer records.

(This version of the story corrects the first, fifth and
third-to-last paragraph after company corrects its statement to say
that 145 million records were accessed, but hackers only copied "a
large part" of that database. Story originally said that hackers
copied the entire database.